Global forest fires. Acid rain. Tsunamis. Skies dark for months or years with volcanic ash. How could anything have survived? Roughly half of all species on Earth died out 65 million years ago. What about the other half? How did they make it?

Not all dinosaurs died out 65 million years ago. Avian dinosaurs-in other words, birds-survived and flourished. Scientists at the American Museum of Natural History estimate that there are more than 18,000 species of birds alive today. A variety of other species also survived on land, including frogs, snakes, lizards and mammals.

A variety of species in the world's oceans, from microscopic organisms to large sharks, survived the mass extinction 65 million years ago. Many organisms living in freshwater lakes and streams were also relatively unharmed—for reasons that aren't clear.